This invention relates generally to radiant, particularly electromagnetic, energy concentration, redirection, and manipulation, and improves over the subject matter of U.S. Pat. No. 4,337,759. It more particularly concerns apparatus and method for employing a transparent lens means with elements thereof using Total Internal Reflection (TIR), in conjunction with a focusing second lens and a wavelength selection filter, for use such as in laser spectrometry.
Radiant energy is redirected to or from a predetermined zone or zones; such redirection having a predetermined degree of concentration and/or chromatic dispersion. The zones have sources of light, as in photoillumination, or radiant energy-receiving means for conversion of the redirected energy to thermal, electric, chemical, or mechanical forms.
The prior art of radiant energy concentration and illumination in general consists of two major types, as exemplified by refractive and reflective astronomical telescopes: a refractive lens, positioned in front of a receiver or light source; or a retro-reflective mirror, positioned behind a receiver or light source. The corresponding devices in the prior art of solar energy concentration are the Fresnel lens and the parabolic reflector, which focus solar energy on a target. Furthermore, there are non-imaging, reflecting concentrators that have the advantage of fixed daily (non-tracking) position with only seasonal adjustments, but the disadvantage of requiring relatively large reflector areas and delivering only relatively low energy concentrations.
Fresnel lenses are devices comprising purely refractive elements, but they have physically inherent limitations of redirecting radiant energy that give high f/ratios and bulky concentrator structure. Moreover, linear Fresnel lenses have, for off-angles in the direction of the grooves, focusing errors, that are also inherent in the laws of refraction, and that limit one-axis tracking configurations to relatively low concentration.
Parabolic reflector concentrators have seen widespread use, but are subject to losses of received radiant energy because the receiver is situated between the source and the reflector, which is thereby shaded, preventing in particular the utilization of large heat engines at the focus. Furthermore, the receiver is exposed to environmental degradation and thermal losses; and the inclusion of a protective, transparent cover means about the receiver will merely reduce the system's optical efficiency.
Another reflecting system has appeared in the literature, as reported by Rabl in Solar Energy, Vol. 19, No. 5. It employs a retro-reflecting means with elements that have two TIR faces to redirect radiant energy out the same side as it came in. Its only improvement over a metal mirror of the same shape is a potentially higher reflectivity; but the double internal reflection doubles the sensitivity to manufacturing error over that of the present invention, which redirects radiant energy through itself with only a single reflection.